1. Field of the Invention
This invention relates to small arms ammunition and, more particularly, to jacketed, boat-tailed bullets.
2. Description of the Related Art
Jacketed bullets include a layer of metal, called a jacket, surrounding at least a portion of a core of the bullet. The core is typically made of lead. It is well known that the heel of a jacketed bullet may be tapered to form what is known as a boat-tail (BT), which acts to enhance the bullet's ballistic stability and to improve the bullet's aerodynamic performance.
Examples of jacketed, boat-tailed bullets can be found in small caliber, 0.5 inch and under, penetrator projectiles used by military forces worldwide. For example, the United States and NATO military forces use vast quantities of M855 cartridges containing 62 grain penetrator bullets, one of which is depicted generally at 10 in FIG. 1. As shown in FIG. 1, the M855 bullet 10 has two aligned cores 12 and 14 enveloped by a brass jacket 16. A steel core 12 is located in a nose section 18 of the bullet 10 and a 32 grain lead core 14 is swaged into a rear section 20. The bullet 10 has a heel that is tapered to form a boat-tail 22, which provides the bullet 10 with ballistic stability and improved aerodynamic performance. In this case, the boat-tail 22 extends from a bearing surface 24 of the bullet 10 to a base 26 of the bullet 10. At a total weight of 62 grains, the M855 bullet 10 has the kinetic energy required to penetrate a 10 gage steel plate when fired from a distance of 600 meters.
In the M885 bullet 10, the steel front core 12 is used to provide the integrity necessary to promote penetration against light armored targets. The lead rear core 14 allows the projectile weight to be obtained using the lowest cost heavy metal available. In addition, the malleable lead material can be conveniently compacted inside the bullet jacket 16 to form a true, cylindrical bearing surface 24 diameter, while producing a consistent form and closure of the boat-tail 22 of the bullet 10. It is this boat-tail 22 forming operation and heel closure that has a significant impact on improving the projectile's stability during launch and, therefore, the accuracy of the bullet 10.
Many of these penetrator rounds are expended at target ranges in military drills. The large volume of lead contained within the projectiles makes environmental reclamation of the target ranges difficult and expensive. Accordingly, various attempts have been made to produce effective lead-free bullets.
For example, U.S. Pat. No. 5,399,187 to Mravic, et al. is directed to lead-free bullets having a density similar to that of lead. The lead-free bullets comprise a compacted composite containing a high-density first constituent selected from the group consisting of tungsten, tungsten carbide, ferro-tungsten and mixtures thereof; and a lower density second constituent selected from the group consisting of tin, zinc, aluminum, iron, copper, bismuth, and mixtures thereof, wherein the density of the lead-free bullet is in excess of 9 grams per cubic centimeter and the lead-free bullet deforms or disintegrates at a stress of less than about 45,000 psi. U.S. Pat. No. 5,399,187 is incorporated by reference herein in its entirety.
In another example, U.S. Pat. No. 6,112,669 to Mravic, et al. is directed to a lead-free projectile made from a composition containing about 5–25% by weight tungsten and more than about 97% by weight tungsten plus iron. U.S. Pat. No. 6,112,669 is incorporated by reference herein in its entirety.
In yet another example, U.S. Pat. No. 6,085,661 to Halverson, et al. discloses a small caliber non-toxic penetrator projectile that has a first core and a second core tandemly aligned and enveloped by a jacket. The first core has a hardness greater than the hardness of the second core, which has a Brinell hardness of between about 20 and about 50. The hardness of the second core is significantly higher than the hardness of lead, and when the first core strikes a target, the second core resists compressive bulging. As a result, more kinetic energy is transferred to the first core rather than being diffused along the surfaces of an armored target. U.S. Pat. No. 6,085,661 is incorporated by reference herein in its entirety.
While various non-toxic metals have proven to be successful replacements for lead in the manufacture of bullets, these non-toxic metals are not without their shortcomings. For example, many non-toxic metals have a hardness greater than lead, which makes the non-toxic metal more difficult to form in the bullet manufacturing process. Where the bullet is to be formed with a boat-tail, excessive material hardness make the mechanical swaging processes utilized in standard bullet manufacture ineffective to form the boat-tail. The boat-tail must then be cut or ground into the rear of the core and, during mechanical enveloping of the jacket around the excessively hard core, there is limited impinging of the jacket with the core. The result is a gap between the jacket and the boat-tail. When this projectile is fired, propellant gasses are forced between the interface of the jacket and the core causing distortion of the jacket and resulting in loss of accuracy and stability. Thus, a new approach is needed to obtain a bullet that is completely devoid of lead while performing ballistically similarly to lead with the manufacturing advantages of lead.